Döring Marius, Lessin Irina, Frenz Theresa, Spanier Julia, Kessler Annett, Tegtmeyer Pia, Dağ Franziska, Thiel Nadine, Trilling Mirko, Lienenklaus Stefan, Weiss Siegfried, Scheu Stefanie, Messerle Martin, Cicin-Sain Luka, Hengel Hartmut, Kalinke Ulrich
Institute for Experimental Infection Research, Twincore, Centre for Experimental and Clinical Infection Research, Hannover Medical School, and Helmholtz Centre for Infection Research, Hannover, Germany.
Department of Vaccinology, Helmholtz Centre for Infection Research, Braunschweig, Germany.
J Virol. 2014 Dec;88(23):13638-50. doi: 10.1128/JVI.00216-14. Epub 2014 Sep 17.
In healthy individuals, the functional immune system effectively confines human cytomegalovirus (CMV) replication, while viral immune evasion and persistence preclude sterile immunity. Mouse CMV (MCMV) is a well-established model to study the delicate CMV-host balance. Effective control of MCMV infection depends on the induction of protective type I interferon (IFN-I) responses. Nevertheless, it is unclear whether in professional antigen-presenting cell subsets MCMV-encoded evasins inhibit the induction of IFN-I responses. Upon MCMV treatment, enhanced expression of MCMV immediate-early and early proteins was detected in bone marrow cultures of macrophages and myeloid dendritic cells compared with plasmacytoid dendritic cell cultures, whereas plasmacytoid dendritic cells mounted more vigorous IFN-I responses. Experiments with Toll-like receptor (TLR)- and/or RIG-I like helicase (RLH)-deficient cell subsets revealed that upon MCMV treatment of myeloid cells, IFN-I responses were triggered independently of TLR and RLH signaling, whereas in plasmacytoid dendritic cells, IFN-I induction was strictly TLR dependent. Macrophages and myeloid dendritic cells treated with either UV-inactivated MCMV or live MCMV that lacked the STAT2 antagonist M27 mounted significantly higher IFN-I responses than cells treated with live wild-type MCMV. In contrast, plasmacytoid dendritic cells responded similarly to UV-inactivated and live MCMV. These experiments illustrated that M27 not only inhibited IFN-I-mediated receptor signaling, but also evaded the induction of IFN responses in myeloid dendritic cells. Furthermore, we found that additional MCMV-encoded evasins were needed to efficiently shut off IFN-I responses of macrophages, but not of myeloid dendritic cells, thus further elucidating the subtle adjustment of the host-pathogen balance.
MCMV may induce IFN-I responses in fibroblasts and epithelial cells, as well as in antigen-presenting cell subsets. We focused on the analysis of IFN-I responses of antigen-presenting cell subsets, including plasmacytoid dendritic cells, myeloid dendritic cells, and macrophages, which are all triggered by MCMV to mount IFN-I responses. Interestingly, myeloid dendritic cells and macrophages, but not plasmacytoid dendritic cells, are readily MCMV infected and support viral gene expression. As expected from previous studies, plasmacytoid dendritic cells sense MCMV Toll-like receptor 9 (TLR9) dependently, whereas in myeloid cells, IFN-I induction is entirely TLR and RLH independent. MCMV-encoded M27 does not impair the IFN-I induction of plasmacytoid dendritic cells, while in myeloid dendritic cells, it reduces IFN-I responses. In macrophages, M27 plus other, not yet identified evasins profoundly inhibit the induction of IFN-I responses. Collectively, these results illustrate that MCMV has evolved diverse mechanisms to differentially modulate IFN-I responses in single immune cell subsets.
在健康个体中，功能性免疫系统有效地限制了人巨细胞病毒（CMV）的复制，而病毒的免疫逃逸和持续性则排除了无菌免疫。小鼠巨细胞病毒（MCMV）是研究CMV与宿主微妙平衡的成熟模型。对MCMV感染的有效控制取决于保护性I型干扰素（IFN-I）反应的诱导。然而，尚不清楚在专业抗原呈递细胞亚群中，MCMV编码的逃避蛋白是否会抑制IFN-I反应的诱导。经MCMV处理后，与浆细胞样树突状细胞培养物相比，在巨噬细胞和髓样树突状细胞的骨髓培养物中检测到MCMV立即早期和早期蛋白的表达增强，而浆细胞样树突状细胞产生更强有力的IFN-I反应。对Toll样受体（TLR）和/或RIG-I样解旋酶（RLH）缺陷细胞亚群进行的实验表明，经MCMV处理髓样细胞后，IFN-I反应的触发独立于TLR和RLH信号传导，而在浆细胞样树突状细胞中，IFN-I的诱导严格依赖于TLR。用紫外线灭活的MCMV或缺乏STAT2拮抗剂M27的活MCMV处理的巨噬细胞和髓样树突状细胞产生的IFN-I反应明显高于用活野生型MCMV处理的细胞。相反，浆细胞样树突状细胞对紫外线灭活的MCMV和活MCMV的反应相似。这些实验表明，M27不仅抑制IFN-I介导的受体信号传导，还逃避了髓样树突状细胞中IFN反应的诱导。此外，我们发现还需要其他MCMV编码的逃避蛋白才能有效阻断巨噬细胞而非髓样树突状细胞的IFN-I反应，从而进一步阐明了宿主-病原体平衡的微妙调节。
MCMV可在成纤维细胞、上皮细胞以及抗原呈递细胞亚群中诱导IFN-I反应。我们重点分析了抗原呈递细胞亚群的IFN-I反应，包括浆细胞样树突状细胞、髓样树突状细胞和巨噬细胞，这些细胞均由MCMV触发产生IFN-I反应。有趣的是，髓样树突状细胞和巨噬细胞而非浆细胞样树突状细胞容易被MCMV感染并支持病毒基因表达。正如先前研究所预期的那样，浆细胞样树突状细胞通过Toll样受体9（TLR9）依赖性地感知MCMV，而在髓样细胞中，IFN-I的诱导完全独立于TLR和RLH。MCMV编码的M27不会损害浆细胞样树突状细胞的IFN-I诱导，而在髓样树突状细胞中，它会降低IFN-I反应。在巨噬细胞中，M27加上其他尚未确定的逃避蛋白会深刻抑制IFN-I反应的诱导。总体而言，这些结果表明MCMV已进化出多种机制来差异调节单个免疫细胞亚群中的IFN-I反应。
